Intake manifold construction, intercoolers

[Craig Dotson]

> Hmm... so why high perf turbo engines have multi-valves heads and high
lift
> cams just as their NA counterparts? If tomorrow the atmosphere pressure
> changes from 101kPa to 202kPa, will this change something to what happens
> inside an engine intake manifold?

Many engines use multi-valve arrangements to increase flow area.  The same
benefits go for a turbo'd car as an NA car in this area...more volume into
the cylinder at a given pressure loss, or the same volume into the cylinder
at a lower pressure loss...at the price of less turbulence.  With more
valves and/or more valve lift you increase the flow area, reducing pressure
loss at a given flow rate.  With more valve duration, the intake valve is
open for a longer percentage of the compression stroke.  If boost pressure
is high enough, more air can be packed into the cylinder even as it starts
the compression stroke, further improving volumetric efficiency.

If atmospheric pressure doubled, I don't think it will make an appreciable
difference in the way an intake manifold worked.  The whole question still
seems inconsequential to me, since by tuning an intake you are trying to
increase intake air pressure by a small number of pascals.  This helps the
engine because the intake pressure becomes slightly higher than exhaust
pressure due to acoustic pressure, helping flow into the cylinder during the
overlap period.  If atmospheric pressure doubled you'd still need to do
this, as exhaust pressure will double accordingly, but with turbocharging
the exhaust pressure increase (it's all absolute pressure here of course) is
small compared to the intake pressure increase.  Tuning the manifold to gain
a small number of pascals pressure will have an insignificant impact when
combined with the already large pressure differential between boost pressure
and exhaust pressure.

Craig Dotson
crdotson at vt.edu
2002 VT FormulaSAE

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org